I’ve never fallen asleep during a lecture (I just can’t) but I constantly do the following: look out of a window and zone out completely, with a lot of daydreaming. It might not be as noticeable as falling asleep, but when the professors do realize that you are not even trying to pay attention they do get pretty angry. I’ll have to try some of your tactics next time it happens.

Definitely a Kodak moment.
You make a good observation. Having a close call (or a spectacular fall!) tends to ramp up our attention level. When I’m feeling particularly tired and sleepy in a class, I will keep nodding off despite my best efforts, and it will just keep getting worse UNTIL I almost fall out of my seat, or the professor calls on someone sitting close to me.
Sometimes I’ve been called on while sleeping. That’s where the “answer a question” strategy came from

There was one time in lectures when someone fell right off their chair with a loud bang (waking them up in spectacular style).

Come to think of it, falling off that chair focused everyone’s attention! But the lecturer wasn’t phased at all. Hopefully he didn’t take it out on the poor guy’s essay marking…